This invention relates to a positioning device which is used for example, to position an arm of an industrial robot, to position a tool, or to operate a machine tool and the like.
The operation of the arm of an industrial robot consists of three kinds of motions: Z-axis motions, .theta.-axis motions and R-axis motions. A Z-axis motion is a vertical motion of the arm, a .theta.-axis motion is a rotational motion of the arm around the support column for the arm; and an R-axis motion is the expansion or contraction of the arm along its length. In order to control these three motions, velocity units are needed in the control unit.
In prior art industrial robots, three velocity units are provided in a control unit, with each of the three velocity units corresponding to one of the above-mentioned three motions.
However, since even a single velocity unit is rather expensive, the number of velocity units tends to make the whole device very expensive, and accordingly limits the availability of industrial robots.
The above-mentioned prior art is disclosed in, for example, the maintenance manual for the FANUC ROBOT MODEL TWO, published by FUJITSU FANUC LTD. The present invention is a proposal to solve the above-described problem existing in the prior art.